136 OKHAMANDAL MARINE ZOOLOGY REPORT PART II 



which is branched. In life, no doubt, the interior of the sponge was filled with soft, 

 pulpy, choanosomal tissue, part of which remains in the form of irregular masses 

 adherent to the inner surface of the cortex, as shown at ch. in Fig. 266. 



The thin cortex is supported internally by a few very stout spicular columns, one 

 of which is shown at sp. c. in the illustrations. No doubt in life these columns, of which 

 I have only been able to find two in the specimen before me, were attached to the 

 substratum, and formed pillars supporting the dome-like cortex. 



The fistulee are very remarkable structures. They have no visible openings, but 

 most of them taper off distally into fine threads, which in three cases are swollen out to 

 form either one or two small buds, as shown at b. in the figures. 



The colour of the cortex (in alcohol) is white, that of the soft internal pulp very 

 pale yellow. 



The greatest diameter of the specimen, at the base, is 17 mm. 



The skeleton may be subdivided as follows : (1) that of the soft internal choano- 

 some or pulp consists of loosely scattered tylostyles or subtylostyles, varying in size 

 but mostly small and often very slender ; (2) that of the internal spicular columns 

 consists of a dense mass of relatively large subtylostyles closely packed together length- 

 wise ; (3) that of the cortex consists of an inner and an outer portion ; the inner portion 

 is a fairly close interlacement of the larger subtylostyles lying tangentially, not much 

 more than one layer thick, with a tendency to the formation of broad bands, which can 

 be seen under a pocket-lens converging towards the bases of the fistular processes ; 

 the outer portion is a thin but rather close pile or fur of short tylostyles or subtylostyles 

 arranged more or less vertically to the surface, with outwardly projecting apices ; ' 

 (4) that of the fistular processes is merely a continuation of the cortical skeleton. The 

 principal bundles of the larger subtylostyles run lengthwise in the wall of the fistula ; 

 where the fistula is drawn out into a solid thread at the end they unite to form a single 

 stout spicular fibre, and in this region the surface-fur of short spicules is almost absent, 

 but becomes strongly developed again when the thread swells out to form a bud. 



Spicules. (1) Subtylostyles of the internal columns and cortex (Fig. 9a) ; straight, 

 slender, tapering gradually to a finely pointed apex, also tapering gradually to the base, 

 where there is usually a very slightly developed head ; the base sometimes appears 

 constricted somewhat suddenly, the " head " being a good deal narrower than the 

 adjacent part of the shaft, as in the specimen figured ; commonly measuring about 

 0-72 by 0-0164 mm. ; (2) small tylostyles (Fig. 9fe) ; chiefly in the surface pile ; usually 

 curved ; apex gradually sharp-pointed ; with rather feebly developed head of smaller 

 diameter than the middle of the spicule ; size about 0-15 by 0-0068 mm. ; (3) spicules 

 of the soft internal pulp ; a mixture of the two kinds already described, together 

 with intermediate forms and very slender forms which are probably young ; perhaps 

 never quite so large as in the spicular columns and cortex, and usually much smaller. 



This species seems to be intermediate in character between the genera Polymastia 



